pseudo_meltdown.c

#include <setjmp.h>
#include <signal.h>
#include <stdio.h>
#include <string.h>

void primer(char probe[256]) {
    // Some specific address
    int addr = 136322;
    // This will throw segmentation fault, but we're "catching it"
    char v = *(char *)addr;
    // This will be executed spectulatively by the CPU
    probe[v] = 1;
}

sigjmp_buf point;

// segfault signal handling
static void handler(int sig, siginfo_t *dont_care, void *dont_care_either) {
   longjmp(point, 1);
}

int main() {
    struct sigaction sa;
    memset(&sa, 0, sizeof(sigaction));
    sigemptyset(&sa.sa_mask);
    
    sa.sa_flags     = SA_NODEFER;
    sa.sa_sigaction = handler;
    sigaction(SIGSEGV, &sa, NULL);

    char probe[256];
    if (setjmp(point) == 0) {
        primer(probe);
    } else {
        printf("Read chunks of probe and check which one is cached\n");
    }

    return 0;
}